Conventional audio amplifiers sometimes include a so-called flying capacitor disposed in a respective switched output stage to drive a load. Typically, the flying capacitor stores an intermediate voltage value whose magnitude is a fraction of a magnitude of a main voltage rail powering the switched output stage. Presence of the flying capacitor enables a controller to apply the voltage of the flying capacitor to a load in addition to being able to apply standard voltage rails such as main power source voltage and ground to the load.
As a more specific example, a main voltage rail of a switched output stage of an amplifier may be 5 volts DC; the voltage on the flying capacitor may be set to ½ the main voltage rail or 2.5 volts DC. When present in an amplifier circuit, the so-called flying capacitor is electrically coupled across multiple switches in a switched output stage (such a sequence of series connected switches configured as a bridge circuit).
As is known, the switches in the switched output stage can be independently controlled to produce an output voltage to drive the load. For example, the switches in the output stage can be controlled (switched ON and OFF at appropriate time) to drive the load with a maximum voltage (main voltage rail) or ground reference voltage at different times.
As mentioned, in addition to having an ability to drive a load with a main voltage rail or a ground reference value, presence of one or more the flying capacitors in a respective drive circuit enables the output stage to drive the load with voltages of the one or more flying capacitors at different times. Thus, via activation of different combination of switches in the switched output stage, a respective controller is able to software between driving a load with voltages of different voltage magnitudes such as a main rail voltage, one or more intermediate or fractional voltages (stored in the one or more flying capacitors), and a ground reference voltage to produce an output voltage to power a respective load.